Boiler with novel gas recirculation arrangement



Nov- 12, 1963 w. H. ARMAc o s'r -3,110,289

BOILER WITH NOVEL GAS RECIRCULATION ARRANGEMENT Filed 001;. 21, 1955 FIG. 2

lNVENTOR WILBUR H. ARMACOST FIG. 3

ATTORNEY Uite tates 3,11%,239 BEEELER Wm Ni) n12 GAS RE ERQUEATEQN ARRANGEMENT This invention relates to vapor generators of the type having upright furnaces into which fuel is fired with the combustion gases passing upwardly through the furnace to an outlet at the upper end thereof and has particular relation to such a vapor generator into the upper portion of the furnace of which recirculated combustion gases are adapted to be controliably introduced.

In modern vapor generators of the so-called utility type the furnace comprises an upright structure, which may be eleven stories high, and which has the inner surface of its walls lined with vapor generating tubes which form a portion of the vapor generating circuit of the generator. Fuel is introduced into the lower portion of this furnace together with the combustion supporting air with the combustion gases generated from the burning of this fuel within the furnace passing. upwardly through the furnace and out a laterally disposed outlet provided at the upper end of the furnace walls. These combus tion gases are conveyed over various convection heat absorbing surfaces, such as superheater surface, economizcr surface, and air heater surface, after which they are discharged into a suitable stack. In order to insure that the combustion gases will be thoroughly mixed prior to passage over the convection heating surface and thereby decreasing the possibility of latu'ng or Stratification of the gas flow over these heating surfaces, a so-called nose bailie is provided at the lower edge of the laterally disposed combustion gas outlet of the furnace. This nose baffle is generally U-shaped and extends well into the furnace and across the entire width of the furnace wall which is provided with the furnace outlet.

It often happens that in vapor generators of this type it is desirable to introduce cooled, recirculated combustion gases into the upper portion of the furnace, with this introduction of cooled gases having the effect of reducing the mean gas temperature leaving the furnace and with this being required in certain boiler designs where th s temperature would otherwise be excessive for proper operation of the boiler and with it also being possible in certain generator designs to control, within limits, superheater vapor temperature by this introduction of combustion gases.

In accordance with the present invention a novel arrangement is provided for introducing these combustion gases into the furnace making use of structure already forming a part of the generator and without the necessity of providing a special distribution duct. As contemplated by the invention the nose bafiie is constructed in such a manner that it comprises a duct extending across the width of the boiler. Spaced uniformly throughout the length of this bathe and preferably at the inner portion thereof and facing generally in a downward direction are a number of openings through which recirculated combustion gases may be introduced into the furnace. Cooled combustion gases are taken from a desired location preferably downstream of a major portion of the convection heating surface, and, through the medium of a fan, are forced into this duct formed by the nose bafiie with these gases being admitted into and distributed across the furnace through the openings provided in this bafile.

it is an object of this invention to provide a vapor geerator into the upper portion of the furnace of which recirculated combustion gases are introduced with there being provided an improved organization for efiecting this introduction of the combustion gases.

Other an further objects of the invention will become apparent to those skilled in the art as the description proceeds.

With the aforementioned objects in view, the invention comprises an arrangement, construction and combination of the elements of the inventive organization in such a manner as to attain the results desired as hereinafter more particularly set forth in the following detailed description of an illustrative embodiment, said embodiment being shown by the accompanying drawing wherein:

FIG. 1 is a vertical section of a vapor generator having an improved gas recirculation organization of this invention.

FIG. 2 is a sectional view through the nose bafiie of the furnace and is taken generally along line 2-2 of FIG. 1.

FIG. 3 is an elevational view of a portion of the nose battle, taken generally from line 33 of FIG. 1 and showing the disposition of the distribution openings throughout the length of the baffle.

Referring now to the drawings, wherein like reference characters are used throughout to designate like elements, the illustrative vapor generator shown therein is comprised of furnace 10 into the lower portion of which fuel and air are introduced through burners 12, which may be of the well known tiltable tangential type, with this fuel being burned within the furnace and the combustion gases thus generated passing upwardly and out the upper end of the furnace. The inner surface of the walls of the furnace it are lined with adjacent, vertically disposed vapor generating tubes 14 which form a portion of the vapor generating circuit of the generator and communicate at their upper ends with steam and water drum 16 and at their lower ends with one of the headers 18, with these headers being connected with drum 16 through a downcomer or downcomers, not shown.

The combustion gases pass from furnace it? through outlet opening 28 provided at the upper end of the rear wall 22 of the furnace with this opening extending across the entire width of this wall. After passing from the furnace the gases are conveyed through duct 24 within which is positioned various convection heat exchange surface of the vapor generator, such as the low temperature superheater section 26 and economizer section 28.

The vapor generated by the vapor generator, which is separated in drum 16 from the liquid circulating through the vapor generating circuit, is superheated by being first passed through the low temperature superheater section 26 and then through the high temperature section 30, with this latter superheater portion being positioned at the upper end of the furnace immediately above nose baffle 32 so that it is shielded by this bafile from a major portion of the radiant heat within the furnace.

This nose bafiie 332 extends into the furnace from the lower edge of outlet opening 24 and across the entire aliases width of the rear wall 22. The vertically disposed tubes which line the inner surface of rear wall 22 are in rather closely spaced relation to each other and, in the illustrative organization, every other tube of this wall 22 is bent inwardly of the furnace and then back toward the plane of the wall so as to formthe ti-shaped baflie 32 with the alternate tubes that are not bent in this manner extending upwardly in the plane of the wall and forming the wall portion 22:: at the rear of this baille with thus being an extension or portion of wall 22. This rear wall portion 22a together with the wall of baffle 32 are constructed and arranged so as to form a duct 34 extending across the entire width of furnace ill for the distribution of cooled recirculated combustion gas-es into the furnace and for this purpose the portions of tubes 14 which are bent from the plane of the wall 22 to form a part of nose baffle 32, and the tubes which form the rear wall portion 22a are provided with fins 33, as is evident from FIGS. 2 and 3, with these fins of adjacent tubes preferably being in abutting relation and welded together so that these walls are substantially gas tight. However, this is only one way in which these walls may be made gas tight and other means and methods well known in the art may obviously be employed if desired.

Combustion gases are introduced into the duct 34 formed by bathe 3'2 and Wall portion 224 by means of motor driven fan 36 the inlet of which communicates with duct 34 at a location downstream of economizer 25 relative to combustion gas flow and the outlet of which communicates with duct 34 through the gas conduit 38 within which is disposed adjustable damper ll The tubes of Wall portion 22a immediately adjacent each side of conduit 33 at the location Where this conduit is connected to this Wall portion have their fins removed and are bent laterally to form an opening for this connection.

In order that the combustion gases conveyed to duct 34 may be introduced into furnace 1rd uniformly across the width of furnace, openings 42 are provided in the wall of ballle 32 by removing a portion of the fin of immediately adjacent tubes with these openings being provided throughout the length of bathe 32 and disposed so that gases issuing therefrom are directed generally downwardly into the furnace but somewhat laterally of the direction of flow of the stream of gases passing up through the furnace. The recirculated gases are thus introduced generally into the center or" the furnace and in a direction somewhat opposed to but at an angle to the upwardly moving gas stream thereby insuring intimate mixing of these recirculated gases with the gases passing upwardly through the furnace and accordingly obtaining a more uniform mean temperature than was heretofore had when combustion gases were recirculated and introduced into the upper portion of the furnace.

Since the nose baffle creates somewhat of a venturi effect because of the reduction in area which is accompanied by an increased velocity and reduced pressure it is advantageous to introduce the recirculated combustion gases adjacent the inner portion of the nose bafile Where the reduction, as a result of this venturi effect, will be greatest so that the power required to operate fan 36 will be at a m'nimum.

When the gas recirculation system is not in operation, damper is closed to prevent the reverse flow of gases through conduit 33 from furnace ll! to the lower portion of duct 24 and accordingly protect fan 36 from being overheated. When it is desired to recirculate gases, however, in order to reduce the mean temperature of the combustion gases which scrub the upper portion of the tubes lining the furnace and pass over the various convection 1 heat exchange surface, fan 36 is activated and darnper dd Lis partially or iully opened.

The amount of and rate at which these gases are recirculated may be controlled by controlling the speed of fan 36 or controlling the position of damper or by both of these methods with these recirculated gases being controlled so as to give the ded sired operating result whether it be to prevent overheating the high temperature superheater section 39 or the portion of the vapor generating tubes in the upper region of the furnace or Whether it be to control the vapor temper ture leaving vapor heater section Ell.

l- /ith this invention the distribution or" recirculated gases across and into the furnace is effected without the necessity of providing a special duct and distribution nozzles or openings associated therewith. in accordance with the invention the nose bafile, which is employed for boilers o the type to which the invention pertains, is constructed il such a manner that it forms a distribution duct thereby eliniina-thig the expense of the special distribution duct heretofore required. Furthermore, by using the nose as a distribution duct, the gases may be introduced into the furnace in such a manner that a more thorough and effective mixing of these recirculated gases with the hot gases passing upwardly through the furnace is assured and the power requirement necessary for efiecting this distribution is maintained at a minimum.

V nil I have illustrated and described a preferred embodiment of my invention it is [to be understood that such is merely illustrative and not restrictive and that variations and modifications may be made therein without departing from the spirit and scope of the invention. 1 therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes as fall within the purview of my invention.

What I claim is:

l. in a vapor generator the combination of an elongated l'urnace of polygonal transverse section, means for introducing fuel and air into the furnace, said furnace having a laterally disposed opening for combustion gases in one of its walls and at a location remote from the location of the fuel and air, the inner surface of the walls of the furnace being lined with immediately adjacent heat exchange tubes extending longitudinally of the furnace', a generally U-shaped nose bathe extending across said onewall and laterally into the furnace generally imme tely upstream of the upstream edge of said opening relative to combustion gas flow, said bafile wall being comprised of tubes that line the inner surface of said one wall are bent from the plane of said wall to form the battle wall with the tubes so bent being uniformly spaced across the wall, the portion of these tubes that form the baflle wall being finned in a manner to close the space between adjacent tubes with openings being provided in at least some of the fins at a location spaced from said one wall and generally uniformly throughout the length of the baffle, said one wall and said baffle forming a duct for conveying combustion gases across the width of the furnace and introducing them into the furnace, and means for conveying combustion gases to said duct.

2. In a vapor generator the combination of an upright furnace of polygonal transverse section and into the generally lower portion of which fuel is introduced and burned, the vertical walls of said furnace including verticaliy disposed heat exchange tubes extending along the inner surface thereof, one of said walls having an opening at its upper end extei ng across substanti lly the entire width of said wall ano forming the combustion gas outlet of the furnace, a generally'U-shaped nose baffle extending across said one wall and laterally into the furnace ge erally immediately upstream of the upstream edge of said ope ing relative to combustion gas flow, said bafile wall havin a generally downward and generally upward portion and being comprised of a portion of the tubes that line the inner surface of said one wall with these tubes being bent from the plane of said wall to for; i the baffle wall with the tubes so bent being generally uniformly spaced across the wall, the portion of these tubes that form the baffle Wall being finned in a manner to close the space between adjacent tubes with the fins being welded together in a substantially fluid tight manner and with openings being provided in the fins on the downward facing portion of the wall and generally uniformly throughout the length of the baffle, the portion of the tubes lining said one wall that are not bent to form said bafile extending between the vertically spaced edges of the bafile and also being finned and Welded together, said one Wall and said bafile forming a duct for conveying combustion gases across the width of the furnace and introducing References Cited in the file of this patent FOREIGN PATENTS Great Britain July 24, 1940 Great Britain July 9, 1952 France Feb. 10, 1954 

1. IN A VAPOR GENERATOR THE COMBINATION OF AN ELONGATED FURNACE OF POLYGONAL TRANSVERSE SECTION, MEANS FOR INTRODUCING FUEL AND AIR INTO THE FURNACE, SAID FURNACE HAVING A LATERALLY DISPOSED OPENING FOR COMBUSTION GASES IN ONE OF ITS WALLS AND AT A LOCATION REMOTE FROM THE LOCATION OF THE FUEL AND AIR, THE INNER SURFACE OF THE WALLS OF THE FURNACE BEING LINED WITH IMMEDIATELY ADJACENT HEAT EXCHANGE TUBES EXTENDING LONGITUDINALLY OF THE FURNACE, A GENERALLY U-SHAPED NOSE BAFFLE EXTENDING ACROSS SAID ONE WALL AND LATERALLY INTO THE FURNACE GENERALLY IMMEDIATELY UPSTREAM OF THE UPSTREAM EDGE OF SAID OPENING RELATIVE TO COMBUSTION GAS FLOW, SAID BAFFLE WALL BEING COMPRISED OF TUBES THAT LINE THE INNER SURFACE OF SAID ONE WALL AND ARE BENT FROM THE PLANE OF SAID WALL TO FORM THE BAFFLE WALL WITH THE TUBES SO BENT BEING UNIFORMLY SPACED ACROSS THE WALL, THE PORTION OF THESE TUBES THAT FORM THE BAFFLE WALL BEING FINNED IN A MANNER TO CLOSE THE SPACE BETWEEN ADJACENT TUBES WITH OPENINGS BEING PROVIDED IN AT LEAST SOME OF THE FINS AT A LOCATION SPACED FROM SAID ONE WALL AND GENERALLY UNIFORMLY THROUGHOUT THE LENGTH OF THE BAFFLE, SAID ONE WALL AND SAID BAFFLE FORMING A DUCT FOR CONVEYING COMBUSTION GASES ACROSS THE WIDTH OF THE FURNACE AND INTRODUCING THEM INTO THE FURNACE, AND MEANS FOR CONVEYING COMBUSTION GASES TO SAID DUCT. 